Assuming no previous programming, story writing or graphic design background...
RenPy for coding. (Install Atom as text editor using RenPy launcher).
Daz3D for creating and rendering 3D CGI style images. (Or Honey Select if Daz3D seems like too much like hard work).
Photoshop or GIMP for graphics editing (for creating UI elements, point-and-click type hotspots or just fixing something that didn't look right when you rendered it).
Grab your 3D assets from this site :
https://f95zone.to/latest/#/cat=assets/page=1/prefixes=33/sort=rating
If you're familiar with 3D modelling... you might prefer Blender for the 3DCG stuff. It is a better tool, but more intermediate user rather than beginner (not that Daz3D is easy either).
If you're art oriented... then maybe do 2D cell shaded type images instead - using whatever art package you're already familiar with.
As for story... Again... assuming no game writing background... Maybe stick to a kinetic novel (no player choices) rather than a visual novel (branching story decisions). Writing and rendering a game is going to be hard enough without learning how to juggle a story that is different depending on the choices made.
If you're new to writing completely and just want to learn the processes... then maybe find a website that has short erotic stories in either written or audiobook form - and try to recreate a story you like (stick to ones that are in one or two rooms max). If you "borrow" their story wholesale - don't sell your game (most small erotic novels are by enthusiastic amateurs like yourself) - maybe don't even publish it. Use it as a way of learning the ropes, so you can write something unique yourself after you've learnt how to do the programming/rendering stuff.
Finally, recognize that "sticking with it" is going to be the hard bit. There's a reason why so many games come out with a 0.1 / demo version and never get another update... it's actually hard work. Spending 3 or 4 months coming up with Chapter 1 is nothing in comparison to the pressure you'll put yourself under trying to create Chapter 2 in only a month.
